The cracking of longitudinal asphalt pavement construction joints is a common pavement distress associated with asphalt pavements. When an asphalt pavement is constructed the width of the pavement is limited by the width of the screed or screed extensions. This width can vary from 8 feet to a maximum of about 35 feet in special cases. Pavement widths that are greater than the maximum screed width require the formation of a longitudinal asphalt pavement construction joint where the hot mix asphalt is paved against the edge of previously laid portion of the pavement. In many situations, the reconstruction of roadways may not allow for full closure to traffic. In such situations which are typical, paving width is limited to one lane (normally 12 feet or 3.6 meters wide) while vehicular traffic is redirected onto an adjacent pavement. This limitation forces the next lane to be placed against the first pavement forming a longitudinal asphalt pavement construction joint between the lanes.
There are a number of deficiencies that are associated with longitudinal asphalt pavement construction joints. For example, the unconfined edges of a first pass of the pavement cannot be compacted to the same degree that the center of the first pass is compacted. Compaction increases density and reduces air voids which are critical to the performance of asphalt pavements. After the first pass is completed an adjacent pass places a hot paving mixture against the now cold first paving pass, creating a longitudinal asphalt pavement construction joint between the two paving passes or lanes.
As a result, the area along the longitudinal asphalt pavement construction joint is higher in air voids, creating permeability to air and water causing the joint to be subject to oxidization and aging more rapidly than the rest of the pavement. The area along the longitudinal asphalt pavement construction joint can be a foot in width where the air voids are higher than the area in the middle of the paving lane. In areas where freeze/thaw occurs, water can intrude into the permeable joint and adjacent area and freeze. As these events occur, the joint becomes significantly weaker than the rest of the pavement, resulting in a greater tendency for the joint to crack from heating and cooling (expansion and contraction) of the adjacent pavement.
Once cracks form along longitudinal asphalt pavement construction joints they allow more water and air to penetrate into the underlying layers of the pavement, causing more damage to the joint and underlying pavement layers. This accelerates the development of fatigue cracks radiating outward from longitudinal cracks which often widens the longitudinal cracks and accelerates the overall damage to the pavement structure.
The initiation of longitudinal asphalt pavement construction joint cracks is caused by the shrinkage of asphalt surface due to pavement heating and cooling cycles from day to night and summer to winter. The cracking occurs at the longitudinal asphalt pavement construction joint because the density of the joint is lower than the rest of the pavement causing a weak bond to be formed. The joint has the lowest tensile strength in the pavement and fails first when the pavement contracts as it cools. A second factor in longitudinal asphalt pavement construction joint cracking is oxidative hardening of the asphalt due to high air voids in the mixture in the joint area which makes that material particularly susceptible to cracking and subsequent raveling. The asphalt mixture adjacent to the longitudinal asphalt pavement construction joint cracking is exposed to air and water intrusion which can lead to poor adhesion between the asphalt and aggregate, which further causes more rapid deterioration (raveling). During early stages, these cracks are usually repaired by sealing. After raveling begins to develop, the repair is more extensive, since the materials adjacent to the crack must be removed and replaced. These maintenance activities are labor intensive and create safety concerns for the maintenance crews since they are usually performed when the pavement is under traffic conditions. This also causes traffic delays for the motoring public.
Longitudinal asphalt pavement construction joint cracking and subsequent raveling degrade pavement serviceability, shorten pavement life and increase life cycle cost. Therefore the reduction or elimination of longitudinal asphalt pavement construction joint cracking results in reduced life cycle costs and increased pavement life.
There are two primary approaches that have been traditionally used to delay longitudinal asphalt pavement construction joint cracking problems. One approach is to make the joint stronger than the adjoining material so that the pavement will not fail at the joint under temperature expansion/contraction. Joint compaction techniques are attempts to prevent cracking in this manner. The second approach to crack prevention is to put very elastic pliable material into the joint during the pavement construction. When this method is used, as the pavement contracts, the joint material simply flows to release the stress.
Mechanical devices have been developed which are intended to compact the unconfined edge of pavement or cut the high air void edge from the pavement. In practice, this approach has not solved the problem of creating a strong joint which lasts as long as the pavement.
Other approaches involve providing an elastic pliable material in the form of a tape at the pavement joint. This tape is placed against a cold longitudinal asphalt pavement construction joint of the pavement. Before use, the joint is cleaned so as to be free of dirt and unbonded material. The edge of the joint tape is then applied to be flush with the surface of the pavement. Next, the non-stick release paper is removed and the placement of the adjacent pavement section is completed. Once the hot mix asphalt is placed against the tape, the tape melts, binding the joint together.
Comparison between pavements installed with joint tape and those installed without a joint tape indicate that the joint tape provides a joint that lasts longer before cracking. The air void content at the immediate area of the joint are reduced and therefore, the joints are less permeable to water. While the joint tape can help address the bond between the adjacent pavement layer and reduce the air voids at the immediate joint face, it fails to address the higher air voids up to a foot away from the joint. Another deficiency of joint tape is the high labor to physically prepare/clean the area and install the material
Studies conducted on highways on a life cycle basis find that pavements in the northern part of the United States develop longitudinal asphalt pavement construction joint cracking within 2 to 3 years after placement of hot mix asphalt. The current treatment strategy is to crack fill the joint with a standard polymerized asphalt or crumb rubber asphalt. The problem is that this topical treatment does not treat the damage caused by water which reaches further into the pavement prior to treatment. Highway departments find that current treatment protocols only last 3 to 4 years after which the crack fill is repeated. Ordinarily pavements currently last 13 years on average. This relatively short 13 year life often is due to damage near the longitudinal asphalt pavement construction joint.
The present invention provides void reducing asphalt membrane compositions and placement that overcome many of the disadvantages associated with known joint materials and installation techniques.